There is an official publication of the Carmelite Order:
The Scapular Of Our Lady Of Mount Carmel-Catechesis and Ritual. Prepared under the direction of the North American Provincials of the Carmelite Orders. This contains the Rite for Blessing of and Enrolment in the Scapular, which requires a priest or a deacon. They say this is the only proper way to be invested with the Scapular. This booklet does have an Imprimatur.

The Brown Scapular of our Lady of Mount Carmel is the habit of the Carmelite Order. The Carmelites recommend:
1. Frequent Mass and reception of Holy Communion.
2. Frequent reading and meditation on the "Word of God"
3. Praying at least part of The Liturgy of the Hours.
4. Imitation of and devotion to Mary
5. The practice of virtues, notably charity, chastity (According to
one's state in life) and obedience to the will of God.

In response to Plato:
Only a priest or deacon may bless a scapular. However, any priest, deacon or person authorized to act in the name of the Order, may enrol others in the Scapular. There are some members of the laity and Religious that have been given authority to act in the name of the Order and to enrol others, but only after the scapular itself has been blessed by a priest or deacon.
Blessings! Polishman